Correcting mistakes

Most DNA mutations occur when your cells divide. But your DNA is also under constant attack from other chemicals in your cells. Fortunately, your cells have a very efficient DNA repair system which is constantly scanning your DNA. Without these DNA repair enzymes, your cells would soon accumulate too much damage to survive. There are two main repair systems: one for removing and replacing a single base-pair mutation, and another for removing long stretches of unwanted, extra base pairs.